Dark Future Predicted for the Universe

Measurements of the recessional velocity, distance and age of stellar explosions called supernovae provided the first direct evidence that the rate at which the universe is expanding is increasing.Credit: NASA.

Empires may
rise and civilizations and ecosystems may crumble in the billions of years to
come, but matter as we know it will endure, according to a new study eyeing the
future of the universe.

The
universe's ceaseless expansion, accelerated by the still-unseen
and mysterious dark energy, will ultimately yield an environment in which matter
nonetheless remains while radiation energy dwindles away, researchers said. The
finding runs contrary to previous thinking that suggested matter would
gradually decay into a radiation-heavy universe.

"Even if
matter begins to decay, it will still be the dominant sort stuff in the
universe," said physicist Lawrence Krauss of Case Western Reserve University,
the lead author of the new study. "That's why I've kind of said that diamonds
are forever."

Future
unlike the past

Krauss and
colleague Robert Scherrer of Vanderbilt University used mathematical models to
determine that in the far future, radiation--including heat, light and all other
forms--will vanish faster than it can be replenished through the decay of matter
into component protons, neutrons and electrons. At the crux of the issue is
dark energy, a hypothetical field or energy which permeates space and tends to
accelerate the universe's expansion.

"It means
that the future isn't like the past, and that the future is once again
different than we thought," Krauss told SPACE.com.

The
research was detailed April 25 in the online edition of the journal Physical
Review D.

Previous
theories suggested that radiation, not matter, would win out in the end because
matter would decay into additional radiation over trillions of years.

"The
universe started out radiation-dominated," Scherrer said in an interview.
"Today, the universe is mostly matter and what's left over from the radiation
is the famous microwave
background, which is very dilute."

Bleak future
for life

Matter may
win out over radiation in the distant future thanks to dark energy, but the odd
force, as-yet unobserved directly, overall paints a bleak and lonely picture
for life as we know it.

"This is
kind of one little small saving grace that we've stumbled across," Scherrer
said of matter's perseverance, adding that current universe forecasts predict a
very cold cosmos in which life will have a hard time surviving.

Over the
next 100 billion years, dark energy is expected to accelerate the most distant
galaxies and stars in the universe beyond the speed of light, meaning that they will
be invisible to future observers. Some objects once visible at half the
universe's current age of about 13.7 billion years are already invisible from
the farthest vantage points, and in about 10 trillion years, only the local
cluster of galaxies, including our own Milky Way, will be visible, researchers
said.

"The future
is bad," Krauss told SPACE.com. "A universe with dark energy is the
worst of all possible universes for the long-term future of life."

After just
one trillion years, Krauss added, astronomers will no longer be able to observe
the universe's expansion, constant microwave background, red shift of galaxies
and other cosmic hallmarks.

"Those are
really all at the basis of our modern understanding of cosmology," said Krauss,
who said he first began theorizing about the future of the universe to discern
how it might end. "People of the future won't be able to know what the universe
is doing."

That puts
astronomers in a unique position today to study the universe, he added.

"I think we
should be buoyed by the fact that it's amazing what we're able to understand
here in this random time in the middle of nowhere in the universe," Krauss
said.